1. Field of the Invention
This specification relates to a unit for sensing a weight of a target to be washed in a washing machine.
2. Background of the Invention
A washing machine is a device for washing laundry, clothes or the like, and has a rotatable drum within a main body thereof. A target to be washed, such as clothes or the like, is stored within the drum and washing water, detergent and the like are then introduced into the drum so as to wash the target to be washed by a rotational force of a pulsator equipped in the drum.
As one example of such washing machines, a drum type washing machine includes a cabinet forming a receiving space, a tub to receive washing water within the cabinet, a drum rotatably disposed within the tub, and a driving motor to rotate the drum.
Among the drum type washing machines, for a certain type that the target to be washed is introduced through a front surface, the tub having a cylindrical shape whose front side is open is disposed within the cabinet. A plurality of springs, each of which has one end connected to an upper surface of the cabinet and is contractible and expandable up and down, may be connected to an upper surface of the tub. A plurality of dampers for reducing vibration generated in a vertical direction of the tub are disposed below the tub. The driving motor is mounted onto a rear side of the tub.
The drum is a cylindrical body rotatably disposed in the tub and receives the target to be washed therein. The driving motor provides a driving force for rotating the drum. The drum is rotated by a rotational force transferred from the driving motor.
In the meantime, the drum type washing machine rotates the driving motor by applying a current to the driving motor in order to sense a weight or an amount of laundry stacked in the drum. Accordingly, a sensor disposed in the driving motor senses a changing level of a rotating speed of the drum, and the sensed value is compared with a previously stored result value, determining the laundry weight.
However, the method of sensing the weight through the driving motor is to merely indirectly determine the weight other than directly measuring it. Consequently, the method has a problem of decreasing accuracy due to various causes, such as positions of the laundry, a characteristic of the driving motor or the like.
Hence, to directly sense the laundry weight within the drum, an approach of sensing the laundry weight by use of a load cell as a weight sensing sensor, which is disposed at a portion contacting a spring installed on the tub, may be used. The load cell which contacts the spring may be transformed due to pressure applied by the spring, and the laundry weight is sensed by electrically sensing a transformed level of the load cell based on strain gages or the like.
However, the case of using the load cell has also a problem of lowering accuracy of sensing the laundry weight, due to a biased transformation of the load cell or the like, which is caused due to non-uniform pressure being applied by the spring, the contact portion between the spring and the load cell being shifted due to vibration generated in response to driving the drum or the like, or the changed posture of the load cell.